TAVARES — Calvin McCullough, blinded by tear gas and exhausted after barricading himself in a three-hour standoff, held a butcher knife to his throat when he faced police on March 24.

''Man, I'm gonna . . . ''

He never finished the sentence.

Two shotgun blasts rang out in the rooming house kitchen, and he fell to the floor.

Leesburg police Sgt. Chris Mullen, who was in the kitchen with McCullough, picked up the knife and tossed it into a sink.

The shotgun, as it turned out, was loaded with nonlethal beanbag rounds. McCullough would live to face charges that he had carjacked a 1996 Plymouth Neon belonging to Allo Hall, 58, an upholstery worker who was on her way to work from her mother's home at Palm Ridge mobile home park.

Detective Pete Ahern testified Wednesday that he went to Leesburg Regional Medical Center to take pictures of self-inflicted cuts on McCullough's wrists.

''It didn't have to end like this,'' the investigator told McCullough after the standoff on Magnolia Street.

Defense attorney Bill Stone was more interested in having Ahern tell jurors about the evidence gathered - and what was not gathered in the case.

Ahern said he did not examine the bedroom where McCullough had barricaded himself. He couldn't explain the backgrounds in crime scene pictures. Some crime scene photos showed a bare floor, similar to the kitchen. Other photos showed carpeting, similar to the bedroom of the apartment.

Lake County Sheriff's evidence technicians were assigned to gather evidence, Ahern said. He also did not go through the car. The investigator added that officers decided it was not necessary to vacuum the he car to search for hairs or other trace evidence.

No one checked to see whether anyone smoked in the car, he said. Hall testified she does not smoke. Stone said some officers detected an odor of smoke in the car.

''Can a cigarette butt be of evidentiary value?'' Stone asked.

Ahern conceded that it is possible to examine traces of saliva for deoxyribonucleic acid, or DNA, a genetic code unique to every individual. Such a match proves to be powerful evidence in a trial.

Police had already testified that it is difficult to get fingerprints from the interior of cars, especially since dashboards frequently are textured. But police said they did find McCullough's fingerprints on the outside of the driver's window and on the trunk, a fingerprint expert testified.

Stone also brought up the appearance that morning of habitual convicted felon Napoleon McCoy. Officer Mike Cassidy, who first spotted the stolen car parked outside a Magnolia apartment house, saw McCoy walking near the car with a plastic bucket full of coins. Police later learned that a bucket like the one under McCoy's arm was taken from the trunk of Hall's car.

McCoy later testified that he had not carried a bucket of coins that day.

Stone called two defense witnesses to the stand, who testified that McCullough had gone to a nightclub in Orlando the night before the carjacking and did not return to Leesburg until daybreak, about the same time as the carjacking.

They said they dropped McCullough off downtown - four miles away from the scene of the crime. However, McCullough's sister, Linda McCullough, said her brother showed up at her home, near the scene of the carjacking, around 6 a.m. The carjacking occurred about 7 a.m.

Stone and Assistant State Attorney Sue Purdy were to begin closing arguments at 9 a.m. today.